Hi @Leigh320 and thanks for posting.
I'm sorry your family member is having problems using the mobile data abroad. Take a look at BT Mobile: I'm having trouble using mobile data abroad and let me know if that helps.
Neil, I tried the Chat Team - not very helpful I must say.
I am in Portugal and have two phones on my account. One roaming working the second not. I checked my account on-line and everything OK. Tried chat and they confirmed that my two phones were set up correctly, but just blamed it on a network error and to try again later - this was despite me telling them that I had beentrying to manually add a moble network for over two days. They seemed oblivious that my other phone was working!
I sorted my second phone by going into mobile networks and resetting to default. Bingo.